In a stalling condition of a motor, if brushes and a commutator of the motor are in a relative position where the brush is close to both of two adjacent segments of the commutator, the two segments may be short-circuited to generate an electric arc between the brush and the commutator, and a large arcing noise may be caused by the electric arc, which is very annoying to end users of the motor. This problem is especially easy to occur in low number of the commutator segments (such as in a 3-bar armature). To avoid such arcing noise, it is necessary to control the relative position between the brushes and the commutator when the motor is in a stalling condition. However, when an operator assembles the motor to a transmission mechanism such as a gear transmission mechanism, the operator cannot observe the commutator and the brushes because they are all mounted within the outer housing. As a result, the operator cannot know the relative position between the brushes and the commutator after the motor driving mechanism is assembled and, therefore, short-circuit of the commutator segments cannot be surely avoided.